There are two forms of alternative hypothesis; directional hypothesis (one-tailed test) and non-directional hypothesis (two-tailed test). In a non-directional hypothesis or two-tailed test the possibility of an effect is described in two directions (Cho & Abe, 2013).Critical region in case of two-tailed test is a result of the collection of values that are less than the first critical values, and these are more than the second critical value. There are several reasons for designing a study with a nondirectional hypothesis. This paper will discuss the reasons for using the non-directional hypothesis by researchers.
Different research situations can make use of non-directional hypothesis or two-tailed test. For example, if a comparison is required between two groups, then the performance of two groups can be assessed using the non-directional hypothesis. But it will not tell how the two groups will be different. Therefore, it will only tell regarding the existence of a relationship between variables but will not specify the direction but will divide the significance level in both directions (Cho & Abe, 2013). Thus, it is addressing all three scenarios that are less than, equal to and greater than and providing accurate and reliable results. It may make use of one or two critical values. Thus, researchers feel that using two-tailed testing is a more rigorous approach to empirical research as results can go in either way.
The two-tailed test has application in production activities also. Research can be carried out to assess the capacity of a particular facility with the help of two-tailed test. It will involve the critical region and will split into two regions. In this way, it will hypothesize the value of the parameter. The results in either of the two directions will consequences refutation of the null hypothesis. If there is no requirement of directional prediction, then two-tailed tests must be used.
Cho, H. C., & Abe, S. (2013). Is two-tailed testing for directional research hypotheses tests legitimate?. Journal of Business Research, 66(9), 1261-1266.